1. Field of the Invention
The invention relates to a flow chamber and a method for detecting low concentrations of molecules produced by cells.
2. Description of the Related Technology
The flow conditions in conventional single compartment flow chambers present difficulties in detecting and measuring cell-produced diffusible molecules, which are typically produced in low concentrations. Diffusible molecules are rapidly carried from the cell surface into the flow current due to convective transport, forming a steep concentration gradient that inhibits the accurate measurement of the diffused molecule concentration. The sensors utilized in conventional flow chambers are also typically unable to make accurate measurements under flow conditions due to the sensor placement and poor flow signal sensitivity. Consequently, single compartment flow chambers are unable to accurately or reliably detect or measure the amount of diffusible molecules produced by cells contained within the single compartment flow chamber.
Specifically, conventional flow chamber systems are incapable of accurately detecting and measuring cell nitric oxide (NO) generated by cells placed under shear stress by contact with a flowing fluid. NO is known to rapidly diffuse and has a short half-life of about 2-30 seconds. Consequently, NO produces sharp gradients in concentration near the source of production due to convective transport which rapidly removes the NO that diffuses into the fluid from the cell surface. The steep concentration gradient and low concentration levels of NO produced by cells make accurate and reliable NO measurements under controlled in vitro conditions virtually impossible. Although, placement of the NO sensing electrodes close to the exposed cell surface can reduce the potential effects discussed above, such an electrode placement will cause disturbances in the flow profile in the vicinity of the cells being monitored thereby altering the results by changing the effective shear stress due to the flow on some or all of the cells. Furthermore, the electrodes used for NO measurement, can also be sensitive to flow, thereby further distorting or masking the NO signal.
Research on shear stress-induced NO production has been severely limited because of the foregoing experimental difficulties and detection limitations on concentration and accuracy. NO detection measured in a system which applies changes in shear stress by changing the fluid flow is particularly challenging because of the low NO concentrations and the many competing phenomena including convection, diffusion, and chemical degradation. Similar problems exist in relation to measurement of other cell-generated species as well.
Consequently, there is a need to develop an improved flow chamber that addresses the deficiencies of the prior art and enables detection and measurement of low concentration cell produced diffusible molecules, such as NO.